SOLAS Sheet Metalworking flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Bend allowance formula

BA = θ × (π/180) × (R + K·T), where θ is the bend angle in degrees, R the inside radius, T the thickness and K the neutral-axis factor. It gives the arc length of the neutral axis used in flat-pattern development.

Bend deduction

Bend deduction equals twice the outside setback minus the bend allowance. Subtracting total bend deduction from the sum of outside leg lengths gives the flat blank length.

Outside setback (OSSB)

OSSB = (R + T) × tan(θ/2), where R is the inside bend radius, T the material thickness and θ the bend angle. It is the distance from the bend tangent point to the outside mould line intersection.

Neutral axis in bending

The layer within a bent sheet that neither stretches nor compresses. Its position, expressed by the K-factor, shifts toward the inside of the bend as the bend radius becomes tighter relative to thickness.

Minimum bend radius

The smallest inside radius that can be formed without cracking the outside surface. It grows with material hardness and thickness and is typically one thickness for mild steel, more for hard alloys.

Bend relief purpose

A notch or slot cut at the end of a bend line that lets material flow during forming. Without it, the flange edge tears or distorts at the corner where the bend terminates.

Sheet metal gauge

A number denoting sheet thickness in a particular standard, where higher numbers mean thinner sheet. Mild steel, galvanised steel and aluminium each have different gauge-to-millimetre tables.

Shearing clearance

The gap between the upper and lower shear blades, usually 5–10% of thickness per side. Correct clearance gives a clean cut; wrong clearance causes burring or edge roll-over.

Work hardening

Increase in strength and loss of ductility caused by plastic deformation during cold forming. It limits how many forming operations a part can take before annealing is needed.

Annealing aluminium 2024

Heating the alloy to roughly 400 °C, holding until uniform, then cooling. It softens the work-hardened metal so further forming does not crack it; natural ageing later re-hardens it.

Rivet edge distance

The minimum distance from a rivet centre to the sheet edge, generally at least twice the rivet diameter. Too small a distance causes tear-out under load.

Pop rivet grip range

The range of total material thickness a blind rivet can clamp. The rivet must be chosen so the stack thickness falls inside this range, otherwise the joint is loose.

Spot weld current rule

Required welding current rises roughly in proportion to sheet thickness, and electrode tip diameter should be about five times the square root of thickness in millimetres.

TIG polarity for aluminium

Aluminium is TIG welded with alternating current, which combines cleaning action on the positive half-cycle with penetration on the negative half. Steel and stainless use direct current electrode negative.

Duct pressure classes

Categories (low, medium, high) that set required seam type, gauge and stiffener spacing. Higher classes demand stronger joints and tighter leakage limits.

Duct leakage factor

Leakage expressed as litres per second per square metre of duct surface at a stated test pressure. The permitted factor depends on the duct pressure class and leakage class.

Shingle-fashion laps

Overlapping sheet so the upper piece laps over the lower in the direction of water flow. This sheds water rather than letting it run into the joint.

Galvanic corrosion

Corrosion caused when two dissimilar metals are in electrical contact in the presence of an electrolyte. The more anodic metal corrodes; isolating the metals prevents it.

Cladding fixing centres

Typical spacing of fasteners along supports, usually 300–600 mm, with fasteners kept at least 25 mm from sheet edges to avoid pull-out and water entry.

Third-angle projection

A drawing convention where the plan is placed below the front elevation and the side view on the side from which it is viewed. Identified by the truncated-cone symbol on the title block.

First-angle projection

A drawing convention where the plan appears above the front elevation and the view on the opposite side. Common in Europe and marked by the appropriate projection symbol.

Datum dimensioning

Dimensioning every feature from a common reference plane or axis rather than from each other. It avoids the accumulation of tolerances that occurs with chain dimensioning.

Worst-case tolerance stack

The total variation when each dimension can be at its limit simultaneously, equal to the sum of the individual tolerances. It is the conservative method for assembly clearance checks.

Statistical tolerance stack

Root-sum-square method: total tolerance = √(t1² + t2² + … + tn²). It assumes independent, normally distributed variations and gives a smaller, less conservative total than worst case.

ISO fit H7/h6

A hole basis clearance fit: upper-case H is the hole tolerance zone, lower-case h the shaft. The shaft is always smaller than the hole, giving a sliding fit.

Vernier least count

Main scale division divided by the number of vernier divisions. A 1 mm main scale with 50 vernier divisions reads to 0.02 mm.

Micrometer least count

Screw pitch divided by the number of thimble divisions. A 0.5 mm pitch with a 50-division thimble gives 0.01 mm resolution.

Surface roughness Ra

The arithmetic mean deviation of the measured profile from its mean line. It is the most common surface texture parameter and is roughly one-quarter to one-fifth of Rz.

Drawing scale 1:5

One unit on the drawing represents five units in reality. A 20 mm measured on the drawing therefore corresponds to 100 mm actual size.

LEV thorough examination

Statutory inspection of local exhaust ventilation at intervals not exceeding 14 months, checking that capture velocity and ductwork still control the hazardous fume or dust effectively.

Welding shade number

Filter shade rises with welding current: about 10 for 60–160 A, 11 for 160–250 A and 12–13 above 250 A on manual metal arc. Gas cutting uses a lighter shade 3–4.

Noise action values

Daily personal noise exposure action values of 80 dB(A) lower and 85 dB(A) upper. At the upper value hearing protection must be worn and the area marked as a hearing protection zone.